Reduce margins for nested lists

[kaitlinnewson]

During the upgrade guide development, it was noted that there is a lot of extra spacing in nested lists (#856). This change should reduce that, and converts the upgrade guide list back into a standard list.

Examples from https://docs.pkp.sfu.ca/accessible-content/en/principles#where-to-add-alt-text

Before change:

After change:

[NateWr]

Looks good. A couple of suggestions. Have you had a quick look at other lists in the docs, just to check that there isn't a negative impact there? Probably fine.

[kaitlinnewson]

Thanks @NateWr, I've incorporated your suggested changes. I have looked across some of the other guides as well where I could find nested lists and haven't noticed any issues (Learning OJS, the Admin guide, the Accessibility guide, the main dev docs, and the Contributors guide).